Autonomic innervation of the cardiovascular system, particularly of the heart, is not complete at birth. There are indications that the vagal innervation is complete, though the sympathetic innervation continues to develop in the first two months of life. This project seeks to investigate in newborn animals: a) the time sequence of the development of autonomic innervation of the heart; b) the nature and extent of its functional maturity; c) the interaction between the sympathetic and parasympathetic systems during the developing phase as related to the heart; and, d) the adaptability of the autonomic control of the heart to stressful situations of hypoxia and acidosis. The time sequence, nature, and extent of autonomic innervation will be examined by direct electrical stimulation of the nerves and analysis of electrical activity of the heart, contractile force of the myocardium at different chamber locations, heart rate, and blood pressure. The interaction between the two systems will be examined by: a) dose-response patterns to autonomic stimulants and depressants; b) analysis of localized electrograms and contractile forces after partial and complete denervation of the heart; c) myocardial vulnerability to dysrhythmias at different stages of autonomic innervation. The adaptability of the autonomic control of the heart will be analyzed by performing above experiments during induced states of hypoxemia and acidosis. The purpose of this investigation is to: 1) determine the development of the autonomic control of specific portions as well as of the heart in total; and 2) to establish any relationship of this developing phase to fatal dysrhythmia and Sudden Infant Death Syndrome. BIBLIOGRAPHIC REFERENCES: Sinha, S.N.; Keresztes-Nagy, S.; and Frankfater, A.: Studies on the distribution of cholinesterases in the human and dog heart. Pediatric Research, 10:754-758, 1976. Yelich, M.R. and Sinha, S.N.: Single premature beat and atrial dysrhythmia in puppies. The Physiologics, 19:419, 1976 (abstract).